Most data storage and retrieval is done by use of magnetic recording apparatus, mainly disc drives and tape drives. In the case of disc drives, there are both "hard" disc and "floppy" disc-type media, the "hard" disc being a rigid platter having a magnetizable surface upon which magnetic flux transitions are recorded by means of a transducer head which aerodynamically "flies" over the surface of the disc, spaced therefrom by a thin film of air. "Floppy" disc drives utilize recording media which is much more in the nature of magnetic tape, being highly flexible. Thus, in floppy disc drives as well as tape drives recording is accomplished by maintaining direct contact between the moving media and the recording head, usually by projecting the tip of the head (at the magnetic "gap") into the plane of the flexible media as it moves past the head. However, tape drives frequently feature bi-directional recording and reproducing operation, and this is not characteristic of disc drives, in which the disc-form media is continuously rotated in the same direction and all recording or reproduction on the media is done unidirectionally.
These fundamental differences in operational characteristics create corresponding fundamental differences in the nature of the transducers or heads which may be utilized, and in order to maximize the likelihood that the read gap will be properly positioned directly over the written track on the media two essentially opposite approaches have come to be recognized in the art with respect to the heads used in tape drives. The first of these involves use of a write gap which is substantially wider than the read gap, such that if the head is anywhere near a centered position with respect to a written track, the read gap is likely to be fully registered with the track, i.e., the recorded transitions will extend across the entire height (i.e., length) of the read gap. The second such approach involves use of a head having a separate erase gap disposed ahead of (i.e., upstream from) the write gap, so that the media is erased cleanly before each writing operation takes place; thus, the writing is always accomplished on media having no residual signals. In this arrangement, a read gap is used which is considerably wider than the written track, so that the entire width of the written track is always likely to be completely straddled by the read gap. Since the separate erase gap eliminates all residual or extraneous signals recorded contiguous to the narrower written track, interference, cross talk and the like will not be present in the read data stream.
Since the approaches just described can only be accomplished with multi-gap heads, they are not utilized in floppy disc drives and many tape drives, where single-gap read/write heads are used. In order to provide a system somewhat analogous to those utilizing separate erase gaps disposed ahead of the write gap, some of these drives utilize a "tunnel erase" concept, in which separate erase gaps are provided on both sides of, and to the rear of, the single read/write gap. The function of the two such erase gaps is to "trim" the marginal edges of the written data track by erasing along both sides thereof, thus producing a resultant narrowed track of written data, the sides of which have no residual or extraneous recorded transitions. In this arrangement, the head structure is somewhat complex since it is necessary to space the erase gaps rearwardly of the read/write gap in order to eliminate or minimize both mechanical and magnetic interference problems, and of course there is the added requirement and expense of providing, and assembling, two separate erase gaps. Furthermore, the tunnel-erase concept is not advantageous in bi-directional recording operations, since that would inherently necessitate the addition of a second pair of erase gaps, spaced on the opposite side of the single read/write gap from the location of the first such set of erase gaps, in order to accommodate both of the possible mutually-opposite recording directions.
In an effort to provide a solution for the difficulties and problems discussed above, it has heretofore been proposed to use a different form of core structure for such transducer heads, which in effect provides operational characteristics functionally representative of those typically found in multi-gap heads, while nonetheless having in fact only a single read/write gap. More particularly, it has been proposed in the past to use a transducer head whose magnetic core structure has a full-width write core disposed on one side of the gap and a partial-width read core on the opposite side of the gap. In this structure, special additional magnetic closure or return pieces are disposed on opposite sides of the comparatively narrow read core at the gap, to in effect fill the space created by narrowing the read core. These additional components serve as part of the write core structure during write procedures but are not intended to contribute to the read core output signal appearing on a sense coil accessing only the read core. For examples of such transducer core structures, reference is made to Japanese Patent Publications Nos. 50-111817 (Pat. No. 5235618) and 58-171710 (Patent Abstracts Vol. 8, No. 10, P. 248), as well as U.S. Pat. No. 4,085,429.
The last-mentioned of the above disclosures discusses the overriding importance of obtaining the most favorable signal-to-noise ratios possible in using such special-purpose transducers, and of isolating the read channel from the write channel therein, and this prior patent is predicated upon the use of certain allegedly critical limitations for the thickness, with respect to the magnetic gap, of isolation layers proposed for use between the narrowed read core and the special additional write core closures disposed on opposite sides of the read core. Notwithstanding this particular factor, however, the prior efforts of others in the field have until now failed to appreciate and take into consideration certain other highly significant factors involved in the special-purpose transducer-head core structure used in such heads which have a very significant effect upon the relative isolation of the write closure from the read core, and the present invention is based on, and provides recognition and disclosure of, certain of these important factors.
Accordingly, the present invention provides new and important structural features and arrangements for a "wide-write, narrow-read" core structure, involving improvements which are of substantial importance in connection with high-density recording operations, and which may in fact ultimately make the difference between successful and unsuccessful high-density recording operation, bearing in mind the underlying requirement that in actual operation digital data recording for data-processing purposes must be substantially free from spurious error and consistently reliable in performance.
Broadly considered, the present invention provides structural improvements and design criteria for "wide-write, narrow-read" magnetic transducer core structures which make possible high-density recording operation with attendant low error rates. More particularly considered, the invention achieves these advantages by providing important structural and positional relationships in the elements comprising the magnetic core; more particularly still, the invention provides certain important size and positioning relationships in the general area of overlap between the read core and the special write core closures which, when carried through by the incorporation of certain preferred arrangements of the special write core closures (laminar elements at times referred to as "strata"), provide the consummately desirable operational results just noted.
The foregoing generalized features of the invention will become more apparent following due consideration of the ensuing specification and the appended drawings, in which a preferred embodiment is disclosed to illustrate the underlying concepts and the overall aspect of the invention .